This is an application for a Mentored Research Scientist Development Award. The candidate's long-term career goal is to become an independent investigator with expertise in the application of biopsychosocial models to individuals with maltreatment experience with an emphasis on social media and social network analysis. Peer influence has been found to be particularly important in the development of both risky sexual activity and substance use. Individuals who have been maltreated are particularly vulnerable. Pubertal maturation has been found to interact with maltreatment to affect risk behaviors. Early maturing adolescents may be more susceptible to peer influence, although this may vary based on maltreatment experience. What has not been examined are the characteristics of social networks that may make maltreated adolescents more vulnerable, and how this influence operates via online interactions. Social network analysis is a viable method for examining these gaps in the literature and there is virtually no research on how maltreated adolescents use social network sites and how this affects their involvement in risky behavior. By examining these relationships across adolescence, we can develop a better understanding of the vulnerabilities for maltreated youth and provide researchers with well-grounded evidence to develop intervention and prevention studies targeting risky sexual behavior and substance use. The proposed study will collect a new wave of social network/social media data to examine the associations between pubertal timing, peer influence, social networks, substance use, and risky sexual behaviors in a sample of maltreated and comparison adolescents. The sample will be drawn from an ongoing longitudinal study of maltreatment on adolescent development. Data on pubertal development, sexual activity, and substance use were obtained at four waves of assessment. The new wave of data collection proposed for this K01 will add to the existing longitudinal study by collecting online social network data and information about the adolescent's current sexual activity and substance use. To complete the proposed research program the candidate will pursue training in four areas: (1) social network analysis, including statistical methods and computer programs for analyzing social networks, (2) the role of social media in adolescent development and how the use of these technologies affects adolescents' interpersonal relationships and behaviors, (3) mechanisms linking maltreatment to risky sexual behaviors and substance use, and (4) biopsychosocial models of development in order to understand how maltreatment, pubertal development, online social interaction, and technology contribute to the development of risky sexual behaviors and substance use. The training and research experience will provide the foundation for the development of an R01 proposal for a longitudinal study integrating puberty, social networks, and risk behavior in a sample of maltreated youth.